Real-Space Visualization of CO₂ Capture, Diffusion, and Release in Surface-Confined Metal-Organic Frameworks

Metal-organic frameworks (MOFs) show significant potential for addressing the urgent demand for high-efficiency carbon dioxide (CO₂) capture and conversion. However, gaining mechanistic insights into CO₂ diffusion processes and host-guest interactions within MOFs remains largely unexplored, due to the challenges associated with atomic-scale imaging. Here, we directly visualize the binding configurations of CO₂ molecules and their dynamic evolution in real space and real time within surface-confined MOFs by combining in situ CO₂ dosing with atomic-resolution scanning probe microscopy. Bond-resolved imaging reveals two distinct CO₂ adsorption configurations, arising from the interactions between flat adsorbed CO₂ and ligand/metal coordination sites of MOFs. Well-organized CO₂ patterns composed of alternating triangular and rhombic subunits are clearly identified within the MOF pores. Temperature-dependent measurements further identify characteristic regimes associated with early stages of CO₂ capture, diffusion, and release. Furthermore, we show how a sudden increase of CO₂ concentration would cause the instability and even collapse of MOFs. These observations highlight the dynamic and nonequilibrium nature of CO₂ capture in surface-confined MOFs and demonstrate the power of real-space approaches for elucidating gas adsorption and diffusion mechanisms at the molecular scale.